ANN ARBOR, Michigan -- Daniel Sturridge scored his first Liverpool goal for eight months and Xherdan Shaqiri netted on his debut as Jurgen Klopp's side beat Manchester United 4-1 in Michigan.

Sturridge, who spent the second half of last season on loan at West Brom, came on in the second half to put Liverpool ahead in front of 101,254 fans at the University of Michigan's Big House after Sadio Mane's penalty and an Andreas Pereira free kick had cancelled each other out.

Sheyi Ojo scored another penalty soon afterwards before Shaqiri, a £13 million summer signing from Stoke, scored with an acrobatic scissor kick to give Liverpool, further ahead in their preseason preparations, a comfortable victory over a young and inexperienced United team.

Jose Mourinho, who handed a debut to £47 million midfielder Fred in the second half, was forced into a change before the game had even kicked off.

United described Smalling's unspecified problem as "minor" and his withdrawal "precautionary" but it is another blow for Mourinho who had been banking on starting the season with a defence of Antonio Valencia, Luke Shaw, Smalling and Bailly.

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Valencia has already flown home with a calf injury while Shaw was also absent from the squad against Liverpool after picking up a knock against AC Milan in Los Angeles.

Liverpool's start was much more smooth and Mo Salah forced Lee Grant into a good save to tip his header over the bar after nine minutes.

United's best moment of the opening 20 minutes was when Mourinho jumped off his seat to catch Grant's miscued clearance prompting a cheer from the Big House crowd.

The next was from the Liverpool fans.

Demetri Mitchell was adjudged to have brought down Salah in the box and Mane stuck the penalty past Grant.

But if Mourinho was worried his young team might crumble after going a goal down, he didn't need to and five minutes later, Pereira curled a beautifully-executed free kick over the wall and beyond Kamil Grabara, in for the injured Lorius Karius.

It brought back memories of Pereira's only senior United goal -- another free kick in a League Cup tie against Ipswich in 2015.

The most interesting thing to happen in the first 15 minutes of the second half was an intruder running onto the pitch.

But he was upstaged on 65 minutes when Shaqiri held up the ball and laid it off for Sturridge to side-foot past Joel Pereira. A first Liverpool goal since November 2017 is not a bad way to remind Klopp he deserves to stay at Anfield this season.

Sturridge thought he might get the chance to grab a second moments later, but when Ander Herrera barged Andy Robertson in the back on 72 minutes, Ojo won the battle for the ball and stroked his penalty past Pereira.

It got even better for Liverpool when youngster Ben Woodburn crossed and Shaqiri's spectacular overhead effort flew into the roof of the net from 10 yards out.